The present invention relates to a self-boring screw having a boring section arranged at the free end of the screw shaft, comprising one or more vanes or cutters, freely projecting perpendicularly in reference to the axis of the screw at an axial distance from the boring tip, with its and/or their edge facing the boring tip being embodied as a boring blade, with the part of the tip of the screw shaft adjacent to the boring section being embodied as a frustum, and with the boring section comprising a chip discharge zone in the section between the vane or the vanes and the part of the tip embodied as a frustum.
Such self-boring screws are known for various specialized applications. Such a self-boring screw is known from EP 0 049 218 A2, having a boring section arranged at the free end of the screw shaft which is fastened at the screw shaft engaging a slot and comprising drill steel or carbide. At an axial distance from the boring tip, one or two vanes are provided at the boring section, freely projecting perpendicularly in reference to the axis of the screw, with their border facing the boring tip being embodied as a boring blade. The screw shaft tapers in a tip, from which the slot extends into the screw shaft. The tip in turn extends on the two large surfaces of the boring section up to the area of the vanes arranged or formed externally at the areas.
A self-boring screw of the type mentioned at the outset, known from the company flyer having the title “Hard or soft wood on high-strength steel sub-frames—for the direct assembly: high-performance boring screws spedec SCT by SFS Stadler” dated 1987, is used to connect wooden and steel plates. Here, the self-boring screw usually first penetrates the wood. Here, vanes are used connected via a predetermined breaking point to the boring section. Their purpose is to expand the drill diameter during the boring process into a wooden layer, sometimes having a thickness of several centimeters, at least to the diameter of the external thread of the thread provided on the screw shaft. The greater the drill diameter is selected for the expanded hole the less friction develops by the wood chips against the thread. This prevents the thread from heating up and thus damages the surface. If then the boring section drills into the next, metallic layer, the vanes break off at their predetermined breaking point and the boring section creates a drill opening fitted for the thread of the screw shaft. In the next step this thread now forms the thread in the drill opening and the screw is tightened. In order to yield an optimum effect, the vanes are usually mounted to the boring section as closely as possible to the screw shaft and thus close to the beginning of the thread. This way it is achieved that the vanes protect the thread in the best-possible fashion and are not eliminated early. For the discharge of the chips, here usually primarily the chips developing by the vanes themselves are considered. The chips produced by the boring tip itself pass through a narrow chip discharge zone between the part of the tip embodied as a frustum and the vane or vanes into the openings created by the vane or vanes and thus they are removed from the boring blade. In all self-boring screws there is the risk of excessive heating of the boring tip because the chips developing at the boring tip cannot be discharged from the boring section by more than the maximally permissible material compression. This in turn can lead to a failed drilling by said self-boring screws.